1. Field of the Invention
The present invention relates to an electronic ink display device, and particularly, to a driving apparatus of a passive matrix type electronic ink display panel and a driving method therefor.
2. Description of the Prior Art
A digital paper display device is being developed as a next generation display device to follow a liquid crystal display device, a plasma display panel, and an organic electro luminescent display device. In particular, an electronic paper using an electronic ink is expected to be a material for replacing the existing printing media such as books, newspapers, magazines, or the like. A display device using the electronic ink is based on an electrophoresis which adds an electric field to a conductive material to allow the material to have a motility, which may be referred to as an electrophoretic display device.
The electronic ink display device distributes particles having a conductivity between thin type flexible substrates and then displays data as a direction setting variation of the particles based on a polarity variation of the electric field. As stated above, the electronic ink display device is a core device for embodying a flexible (or paper) display device because the device can be created by a flexible substrate.
Once creating the electronic ink display device in a form of panel by using a substrate of a flexible material, the electronic ink display device can be created flexibly, and also can be easily carried by constructing it in a thin type. Furthermore, the electronic ink display device has a simple electrode structure, and its manufacturing process is also simple, thereby producing it with low costs. The electronic ink display device is easy to scale it up, and consumes a small amount of power because of not using a back light. On the other hand, the electronic ink display device delays a response time because data is displayed depending on motions of particles. As a result of this, it is not suitable to embody a moving image. The electronic ink display device also has a limitation to represent a full color and a gradation.
Hereinafter, it will be explained of an architecture of the electronic ink display device and an operating principle thereof, and a driving apparatus of a passive matrix type display device and a method therefor with reference to FIGS. 1 to 4.
FIG. 1 is a sectional view showing a cell of the electronic ink display device of the conventional art.
Referring to FIG. 1, the cell of the electronic ink display device of the conventional art includes: an upper substrate 10 and a lower substrate 80 made of plastic or glass; an upper electrode 20 placed at a lower surface of the upper substrate 10, for applying a driving voltage to a capsule 60 and a lower electrode 70 placed at an upper surface of the lower substrate 80, for applying the driving voltage to the capsule 60; and the capsule 60 placed between the upper electrode 20 and the lower electrode 70. Here, in the capsule 60, white pigment particles 30 and black pigment particles 50, and dielectric fluid 40 are encapsulated.
If an electric field is formed between the upper electrode 20 and the lower electrode 70 by applying a voltage to the upper electrode 20 and the lower electrode 70, such constructed cell can embody white and black colors by moving the black pigment particles and white pigment particles based on the formed electric field. That is, if a positive voltage is applied to the upper electrode 20 and a negative voltage is applied to the lower electrode 70, the white pigment particles 30 are attracted to the upper electrode 20 and the black pigment particles 50 are attracted to the lower electrode 70, and thereby the cell displays a white color. Contrarily, if the negative voltage is applied to the upper electrode 20 and the positive voltage is applied to the lower electrode 70, the white pigment particles 30 are attracted to the lower electrode 70 and the black pigment particles 50 are attracted to the upper electrode 20, and thereby the cell displays a black color.
FIG. 2 is a sectional view showing an RGB pixel of the electronic ink display device of the conventional art.
Referring to FIG. 2, one RGB pixel of the conventional art is comprised of respective three cells described in FIG. 1 as a sub-pixel. An R cell displays red, a G cell displays green and a B cell displays blue. Here, if a negative voltage is applied to an upper electrode 21 and a positive voltage to a lower electrode 71, a voltage is not applied to both an upper electrode 22 and a lower electrode 72. If a positive voltage is applied to an upper electrode 23 and a negative voltage is applied to a lower electrode 73, each cell will be operated as follows. Because the negative voltage is applied to the upper electrode 21, the black pigment particles (MBL) in the R cell are attracted to the upper electrode 21. On the other side, because the positive voltage is applied to the lower electrode 71, the red pigment particles (MR) in the R cell are attracted to the lower electrode 71, and thereby the R cell displays black. Furthermore, because the voltage is not applied to both the upper electrode 22 and the lower electrode 72, the green pigment particles (MG) and the black pigment particles (MBL) in the G cell may be mixed randomly, or maintain the existing state. Also, because the positive voltage is applied to the upper electrode 23, the blue pigment particles (MB) in the B cell are attracted to the upper electrode 23, and because the negative voltage is applied to the lower electrode 73, the black pigment particles (MBL) in the B cell are attracted to the lower electrode 73, and thereby the B cell displays blue.
At this time, each cell is sensitively reacted according to a size of voltage applied between the upper electrodes 21, 22 and 23 and the lower electrodes 71, 72 and 73. Thus, if a simple matrix driving method based on the conventional art is used, there may occur a difference in an amount of attracted pigments particles and a moved speed of the pigment particles.
Hereinafter, it will be explained of an operation of the electronic ink display device when the simple matrix driving method based on the conventional art is used for a passive matrix type electronic ink display device with reference to FIGS. 3 and 4.
FIG. 3 is a waveform diagram showing a voltage applied to the passive matrix type electronic ink display device to which the simple matrix driving method based on the conventional art is applied.
Referring to FIG. 3, according to the simple matrix driving method based on the conventional art, a scan pulse which is varied from a predetermined negative voltage −Vs to a ground voltage 0V is applied to a cell connected to a first scan line SL1 in a display panel (not shown) in which a plurality of data lines D1˜Dm and a plurality of scan lines SL1˜SLn are constructed in a matrix type. Then, while the scan pulse is applied, a data pulse of a predetermined positive voltage VD is applied to data lines selected among the plurality of data lines constructed in the display panel, thereby operating cells. Furthermore, the ground voltage 0V is applied to the remaining scan lines without the scan pulse applied, which processes are executed for every scan lines. Thereafter, once all cells are operated, a reset pulse of a predetermined negative voltage −Vr is applied to all of the data lines D1˜Dm. As a result of this, the display panel becomes a black state.
However, unlike existing display devices, because there is not any threshold voltage in the electronic ink display device, there can occur a problem that the color pigment particles in the capsule can be moved due to somewhat voltage applied even to a cell which should not be driven. Therefore, the electronic ink display device can not be passively driven by the simple matrix driving method based on the conventional art.
Now, it will be explained of problems when the simple matrix driving method based on the conventional art is applied to the electronic ink display device with reference to FIG. 4.
FIG. 4 is a wave form diagram showing a voltage applied to a cell during a time A shown in FIG. 3.
Referring to FIG. 4, a driving voltage Va is applied to cells of a first scan line SL1 to which a data pulse and a scan pulse are simultaneously applied to be operated normally. However, a voltage lower than the predetermined voltage Va (applied to the cells of the first scan line SL1) is applied to cells (to which the data pulse is applied but the scan pulse is not) of the remaining scan lines SL2˜SLn. Therefore, the color pigment particles in the capsule of the cell are slowly moved within the capsule. As a result, because a voltage representing a data signal is applied to a scan electrode of another cell other than a cell to be driven, the electronic ink display device can not be driven normally when using the simple matrix driving method based on the conventional art therefor.
As aforementioned, when applying the simple matrix driving method based on the conventional art to the electronic ink display device, unlike existing display devices, because there is not a threshold voltage which determines whether to drive a cell in the electronic ink display device, a voltage having a smaller value than a predetermined value applied to the data lines is applied to cells other than the cell to be driven. As a result, there can occur a problem that other cells except the cell to be driven may be also driven.
Due to those problems, an active matrix type electronic ink display device is being developed. However, the active matrix type electronic ink display device has a complicated manufacturing process and a complicated driving method therefor, and consumes a large amount of power, comparing to the passive matrix type electronic ink display device.